A mouse model of the slow channel myasthenic syndrome: Neuromuscular physiology and effects of ephedrine treatment.

In the slow channel congenital myasthenic syndrome mutations in genes encoding the muscle acetylcholine receptor give rise to prolonged ion channel activations. The resulting cation overload in the postsynaptic region leads to damage of synaptic structures, impaired neuromuscular transmission and fatigable muscle weakness. Previously we identified and characterised in detail the properties of the slow channel syndrome mutation εL221F. Here, using this mutation, we generate a transgenic mouse model for the slow channel syndrome that expresses mutant human ε-subunits harbouring an EGFP tag within the M3-M4 cytoplasmic region, driven by a ~1500 bp region of the CHRNB promoter. Fluorescent mutant acetylcholine receptors are assembled, cluster at the motor endplates and give rise to a disease model that mirrors the human condition. Mice demonstrate mild fatigable muscle weakness, prolonged endplate and miniature endplate potentials, and variable degeneration of the postsynaptic membrane. We use our model to investigate ephedrine as a potential treatment. Mice were assessed before and after six weeks on oral ephedrine (serum ephedrine concentration 89 ± 3 ng/ml) using an inverted screen test and in vivo electromyography. Treated mice demonstrated modest benefit for screen hang time, and in measures of compound muscle action potentials and mean jitter that did not reach statistical significance. Ephedrine and salbutamol show clear benefit when used in the treatment of DOK7 or COLQ congenital myasthenic syndromes. Our results highlight only a modest potential benefit of these ß2-adrenergic receptor agonists for the treatment of the slow channel syndrome.

Distinct phenotypes of congenital acetylcholine receptor deficiency.

We contrast the phenotypes associated with hereditary acetylcholine receptor deficiency arising from mutations in either the acetylcholine receptor epsilon subunit or the endplate acetylcholine receptor clustering protein rapsyn. Mutational screening was performed by amplification of promoter and coding regions by PCR and direct DNA sequencing. We identified mutations in 37 acetylcholine receptor deficiency patients; 18 had acetylcholine receptor-epsilon mutations, 19 had rapsyn mutations. Mutated acetylcholine receptor-epsilon associated with bulbar symptoms, ptosis and ophthalmoplegia at birth, and generalized weakness. Mutated rapsyn caused either an early onset (rapsyn-EO) or late onset (rapsyn-LO) phenotype. Rapsyn-EO associated with arthrogryposis and life-threatening exacerbations during early childhood. Rapsyn-LO presented with limb weakness in adolescence or adulthood resembling seronegative myasthenia gravis. Awareness of distinct phenotypic features of acetylcholine receptor deficiency resulting from acetylcholine receptor-epsilon or rapsyn mutations should facilitate targeted genetic diagnosis, avoid inappropriate immunological therapy and, in some infants, prompt the rapid introduction of treatment that could be life saving.

Rapsyn mutations in hereditary myasthenia: distinct early- and late-onset phenotypes.

Rapsyn mutations in 16 unrelated patients with a congenital/hereditary myasthenic syndrome were identified, and a mutation (N88K) common to each of them was found. Two distinct phenotypes were noted: early and late onset. The former is frequently associated with arthrogryposis multiplex congenita and life-threatening crises. The late-onset phenotype developed in adolescence or adulthood and was initially mistaken for seronegative myasthenia gravis. Recognition of this late-onset phenotype should prevent inappropriate immunotherapy.

Glial growth factor 2 induces proliferation and structural changes in ensheathing cells.

Ensheathing cells were isolated from neonatal rat olfactory bulbs and cultured in the presence of glial growth factor 2 (GGF2). Proliferation assay showed that at concentrations of up to 60 ng/ml GGF2, ensheathing cells underwent a modest increase in proliferation rate. This stimulation was not maintained at high doses of GGF2 at 100 ng/ml or more. Chemotaxis chambers and scanning electron microscopy were used to determine whether GGF2 was a chemoattractant for ensheathing cells. Although the results showed no chemotactic response to GGF2, ensheathing cells demonstrated structural changes when cultured in the presence of 20 ng/ml GGF2. Ultrastructural observations revealed that GGF2 promoted increased deposition of extracellular matrix on the cell membrane, more cytoskeletal elements in the processes and as a possible consequence, contributed to a more rigid support. Ensheathing cells cultured in the absence of GGF2 often extended thinner and curved processes. Reverse transcription-polymerase chain reaction confirmed the presence of GGF2 transcripts in ensheathing cells, suggesting that ensheathing cells themselves are a source of GGF2.

The synthesis of novel matrix metalloproteinase inhibitors employing the Ireland-Claisen rearrangement.

Matrix metalloproteinase inhibitors of general formula (1) were synthesised by a route involving an Ireland-Claisen rearrangement which enables systematic modification of the substituent alpha to the hydroxamic acid. An analogue (12c) possessing an alpha-cyclopentyl group is a potent broad spectrum inhibitor that displays high and sustained blood levels following oral dosing in both the rat and marmoset ex-vivo bioassays. This compound and analogues are also potent inhibitors of TNF alpha release.

Matrix metalloproteinase expression during experimental autoimmune encephalomyelitis and effects of a combined matrix metalloproteinase and tumour necrosis factor-alpha inhibitor.

Matrix metalloproteinases (MMPs) are a large family of Zn2+ endopeptidases that are expressed in inflammatory conditions and are capable of degrading connective tissue macromolecules. MMP-like enzymes are also involved in the processing of a variety of cell surface molecules including the pro-inflammatory cytokine TNF-alpha. MMPs and TNF-alpha have both been implicated in the pathology associated with neuro-inflammatory diseases (NIDs), particularly multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE). We have shown that BB-1101, a broad spectrum hydroxamic acid-based combined inhibitor of MMP activity and TNF processing, reduces the clinical signs and weight loss in an acute EAE model in Lewis rats. However, little is known about which MMPs are involved in the neuroinflammatory process. In order to determine the optimum inhibitory profile for an MMP inhibitor in the treatment of NID, we investigated the profile of MMP expression and activity during EAE. The development of disease symptoms was associated with a 3-fold increase in MMP activity in the cerebrospinal fluid (CSF), which could be inhibited by treatment with BB-1101, and an increase in 92 kDa gelatinase activity detected by gelatin substrate zymography. Quantitative PCR analysis of normal and EAE spinal cord revealed the expression of at least seven MMPs. Of these, matrilysin showed the most significant change, being elevated over 500 fold with onset of clinical symptoms and peaking at maximum disease severity. Of the other six MMPs detected, 92 kDa gelatinase showed a modest 5 fold increase which peaked at the onset of clinical signs and then declined during the most severe phase of the disease. Matrilysin was localised by immunohistochemistry to the invading macrophages within the inflammatory lesions of the spinal cord. Matrilysin's potent broad spectrum proteolytic activity and its localisation to inflammatory lesions in the CNS suggest this enzyme could be particularly involved in the pathological processes associated with neuro-inflammatory disease.

Enhanced expression of MMP-7 and MMP-9 in demyelinating multiple sclerosis lesions.

The pathology of multiple sclerosis (MS) is characterised by breakdown of the blood-brain barrier accompanied by infiltration of macrophages and T cells into the central nervous system (CNS). Myelin is degraded and engulfed by the macrophages, producing lesions of demyelination. Some or all of these mechanisms might involve proteinases, and here we have studied the cellular localisation and distribution of two matrix metalloproteinases (MMPs), MMP-7 (matrilysin) and MMP-9 (92-kDa gelatinase), in the normal human CNS and active demyelinating MS lesions. Cryostat sections of CNS samples were immunostained with antisera to MMP-7 and MMP-9. In addition, non-radioactive in situ hybridisation (ISH) was performed using a digoxygenin-labelled riboprobe to detect the expression of MMP-7. MMP-7 immunoreactivity was weakly detected in microglial-like cells in normal brain tissue sections, and was very strong in parenchymal macrophages in active demyelinating MS lesions. This pattern of expression was confirmed using ISH. MMP-7 immunoreactivity was not detected in macrophages in spleen or tonsil indicating that it is specifically induced in infiltrating macrophages in active demyelinating MS lesions. MMP-9 immunoreactivity was detected in a few small blood vessels in normal brain tissue sections, whereas many blood vessels stained positive in CNS tissue sections of active demyelinating MS lesions. The up-regulation of MMPs in MS may contribute to the pathology of the disease.

Quantitation of matrix metalloproteinases in cultured rat astrocytes using the polymerase chain reaction with a multi-competitor cDNA standard.

Matrix metalloproteinases (MMPs) are a family of Zn2+ endopeptidases that are expressed in many inflammatory conditions and that contribute to connective tissue breakdown and the release of the pro-inflammatory cytokine tumour necrosis factor-alpha (TNF-alpha). There is emerging evidence that MMPs have a role in inflammatory disorders of the central nervous system (CNS) such as multiple sclerosis. However, little is known about the expression of MMPs by inflamed tissue within the CNS or by the glia, neurones, and leucocytes which participate in the inflammatory response. To address this issue we have developed a polymerase chain reaction (PCR)-based method for the quantitation of rat MMP mRNA levels, which we have applied to astrocyte cultures with and without inflammatory stimulation. The technique relies on a competition reaction in which a synthetic standard cDNA is co-amplified with the target cDNA in the same PCR reaction. Standard multi-competitor cDNAs, containing priming sites for nine MMPs, and two housekeeping genes were constructed. We have shown that MMP activity is increased over three-fold in neonatal rat astrocyte cultures following stimulation with lipopolysaccharide (LPS). At the mRNA level, MT-MMP-1, 72 kDa gelatinase, and stromelysin-3 were constitutively expressed and unaffected by LPS treatment, whereas 92 kDa gelatinase, and stromelysin-1 were strongly induced (1,000-fold). Stromelysin-2, rat collagenase, and macrophage metalloelastase were modestly upregulated by LPS treatment. Matrilysin was not expressed. This technique is suitable for quantifying MMP expression in the cells which contribute to inflammation in the CNS and could also be applied directly to tissue samples from animal models of disease.

Macrophage metalloelastase degrades matrix and myelin proteins and processes a tumour necrosis factor-alpha fusion protein.

The matrix metalloproteinases (MMPs) are a group of enzymes which have the ability to degrade extracellular matrix. They also cleave non-matrix proteins such as myelin basic protein and alpha 1-antitrypsin and they are able to process tumour necrosis factor-alpha (TNF) to its mature form. We have cloned, expressed and purified human macrophage metalloelastase (EC 3.4.24.65), an MMP recognised for its ability to degrade elastin, but whose substrate specificity has not yet been defined. With the exception of type I collagen this enzyme degraded all matrix proteins tested, namely: type IV collagen, type I gelatin, fibronectin, laminin, vitronectin and proteoglycan. It also degraded myelin basic protein, cleaved alpha 1-antitrypsin and released TNF from a pro-TNF fusion protein. Thus, in common with several other MMPs, macrophage metalloelastase has a broad substrate range which extends beyond that of elastin alone.

Identification of MMP-18, a putative novel human matrix metalloproteinase.

A partial cDNA encoding the 3' end of a putative novel human matrix metalloproteinase (MMP) was identified by sequence similarity searching of databases containing expressed sequence tags. The remaining 5' end of the MMP cDNA was amplified by PCR from human mammary gland cDNA. The predicted protein product displays all the structural features characteristic of the MMP family and has closest identity with MMP-1, -3, -10, and 11. We have provisionally designated this novel MMP as MMP-18. MMP-18 mRNA is expressed in a wide variety of normal human tissues, including mammary gland, placenta, lung, pancreas, ovary, small intestine, spleen, thymus, prostate, testis, colon, and heart, but is not detected in brain, skeletal muscle, kidney, liver, or peripheral blood leucocytes.

Peptides shorter than a minimal CTL epitope may have a higher binding affinity than the epitope for the class I Kk molecule.

A previously published Kk-specific motif was used to predict that an optimal Kk-restricted epitope within the nucleoprotein (NP) of influenza A/PR/8/34 virus corresponds to sequence SDYEGRLI (residues 50-57). Although this is the minimal epitope recognized by murine cytotoxic T lymphocytes (CTL), its binding affinity for the Kk molecule is increased following removal of either the N-terminal amino acid residue (S) or the N-terminal dipeptide (SD). A possible explanation for this unexpected result is that interactions between the C-terminus of the epitope and the Kk molecule contribute to the binding energy to a much greater extent than interactions between the N-terminus of the epitope and the Kk molecule.

Precise prediction of a Kk-restricted cytotoxic T cell epitope in the NS1 protein of influenza virus using an MHC allele-specific motif.

The nonstructural protein NS1 of influenza A/PR/8/34 virus has previously been reported to be recognized by murine Kk-restricted cytotoxic T lymphocytes (CTL), although the sequence of the epitope was not defined. A Kk-specific motif has previously been published and consists of a glutamic acid or (less frequently) an aspartic acid at position 2 and an isoleucine at the carboxyl terminus of a peptide eight or nine residues long. This motif was used here to predict the sequence of the NS1 epitope, which was defined as a nonapeptide corresponding to amino acid residues 152-160, sequence EEGAIVGEI. This is the first CTL epitope to be defined within the NS1 protein of the influenza A virus. A model of how this epitope could bind to the Kk molecule was produced by homology modelling from an X-ray crystal structure of a human HLA/peptide complex.

A 15 amino acid fragment of influenza nucleoprotein synthesized in the cytoplasm is presented to class I-restricted cytotoxic T lymphocytes.

A recombinant vaccinia has been designed to express amino acids 366-379 of influenza nucleoprotein, previously shown to be the minimal epitope recognized by a class I-restricted cytotoxic T cell clone. Target cells infected with the recombinant vaccinia virus expressing this peptide are recognized by CTL as efficiently as target cells expressing the complete nucleoprotein. The results imply the existence of a peptide transport system that constitutively passes the products of degraded proteins from the cytoplasm into a membrane-bound compartment of the cell.